The present invention relates generally to a hermetic refrigerant compressor such as may be driven by an electric motor supported within a hermetically sealed housing. More particularly, the invention relates to a lubrication system for such compressor wherein advantage is taken of the rotation of a shaft driven by the motor for lubricating parts of the compressor. Typically, for a lubrication system of this type, the compressor motor is oriented so the driven shaft extends vertically downward with the lower end portion of the shaft being immersed in a sump of lubricant collected in the lower section of the housing. With the lower end portion of the shaft constructed as a pump impeller to form a lubricant pumping means, when the motor is running, lubricant may be pumped upwardly through the system to lubricate between the parts of the compressor which are moving relative to each other.
In prior art hermetic refrigerant compressors, such as those disclosed in U.S. Pat. No. 3,584,980 and in U.S. Pat. No. 3,926,281, the lower end portion of the driven shaft may be adapted to function as a two-stage pump. One reason for using two-stage pumping is to develop sufficient flow and pressure in the discharged lubricant for lubricating the less accessible upper parts of the compressor. This is particularly important in a multiple-speed compressor which is powered by an electric motor that is adapted to be switched selectively between two-pole and four-pole operating modes according to the speed desired for operation of the compressor. With the motor operating in its two-pole mode, its speed is, of course, twice that of when operating in its four-pole mode. Accordingly, the quantity of lubricant and the pressure within the lubricant being pumped by the rotating shaft is substantially different for the two modes of operation.
Even with the increased flow and pressures provided by two-stage pumping, difficulty may be encountered in obtaining adequate lubrication of the support bearings for the motor. This is because some of the refrigerant used in the compressor is naturally absorbed in the lubricant and, as the lubricant is pumped through the system, the absorbed refrigerant tends to flash or boil out of the lubricant as lubricant pressure decreases and/or the temperature increases. Undesirably, the flashed refrigerant gases may collect within the passages of the lubricating system, creating a pressure barrier to the adequate flow of lubricant to the working parts of the compressor. This is particularly true at the upper support bearings for the motor shaft because of the increase in the temperature of the lubricant and the loss of pressure as the lubricant is pumped through a discharge conduit leading upwardly toward the motor and into an annular chamber from which the upper bearing surfaces are lubricated.